Cavity reflector light injection for flat panel displays

ABSTRACT

A light mixing system includes a transparent waveguide having a reflectorized edge, a light input edge and a light output edge opposite the reflectorized edge. The light input edge receives light of different colors from two or more light sources. The received light of different colors is totally internally reflected from opposite major surfaces of the waveguide. Formed inside the waveguide are a plurality of cavities bounded by walls substantially parallel to the edges and substantially orthogonal to the major surfaces of the waveguide. Interaction of the received light of different colors with one or more of the cavities and the reflectorized edge mixes the light of different colors before exiting the light output edge.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/574,700, filed Oct. 6, 2009, which claims priority to U.S.Provisional Patent Application No. 61/103,193, entitled “CavityReflector Light Injection for Flat Panel Displays”, filed on Oct. 6,2008, the entire disclosures of both of which are herein incorporated byreference.

TECHNICAL FIELD

The present application relates to the field of flat panel displays, andmore particularly to providing a light mixing means to enhance thevisual performance of transmissive flat panel displays that utilize anedge-illuminated transparent slab waveguide to provide light to thepixel shuttering mechanisms that perform image modulation on the displaysurface. The range of applicability of the present disclosure is notlimited to direct view systems such as flat panel displays or waveguidebacklights, but can also be deployed in projection-based displaytechnologies.

BACKGROUND INFORMATION

Various flat panel display systems have been developed over the lastseveral decades. Among them is the Time Multiplexed Optical Shutterdisclosed in Selbrede U.S. Pat. No. 5,319,491 (which is incorporated inits entirety herein) and such variations as have been subsequently filedin commonly owned U.S. Pat. Nos. 7,042,618, 7,057,790, 7,218,437,7,486,854 and U.S. Patent Publication No. 2008/0075414. The fundamentalpremise of such devices is that light (usually monochromatic light) isedge-injected into a transparent rectangular slab waveguide such thattotal internal reflection (TIR) of the injected light obtains within thewaveguide, which may be mirrored on one or more of the side surfaces toinsure maximum transits for rays traveling within the waveguide. Theprinciple of operation for any of the plurality of pixels distributedacross the slab waveguide involves locally, selectively, andcontrollably frustrating the total internal reflection of light boundwithin the waveguide to emit light at that pixel location. In one pixelarchitecture, frustration of TIR light bound within the waveguide isachieved by propelling (i.e., moving) an optically-suitable materialacross a microscopic gap, such that the material is at or near contactwith a surface of the slab waveguide in the active position, while inthe inactive position the material is sufficiently displaced from thesurface of the waveguide so that light and/or evanescent coupling acrossthe gap is negligible. The optically-suitable material, herein referredto as an “active layer”, being propelled (i.e., moved) can be anelastically deformable thin sheet (thin layer or film) of polymericmaterial (e.g., elastomer) with a refractive index selected to optimizethe coupling of light during the contact/near-contact events. Switchingthe active layer between inactive and active positions can occur at veryhigh speeds in order to permit the generation of adequate gray scalelevels for multiple primary colored light (e.g., consecutive primarycolored lights red-green-blue) at video frame rates in order to avoidexcessive motional and color breakup artifacts while preserving smoothvideo generation. The flat panel display is thus comprised of aplurality of pixels, each pixel representing a discrete subsection ofthe display that can be individually and selectively controlled inrespect to locally propelling the active layer bearing a suitablerefractive index across a microscopic gap into contact or near contactwith the slab waveguide. The propulsion can be achieved by theelectromechanical and/or ponderomotive deformation of the thin sheet ofpolymeric material, said sheet being tethered at the periphery of theindividual pixel geometry by standoffs that maintain the sheet in asuitable spaced-apart relation to the slab waveguide when the pixel isin the quiescent unactuated state. Application of an appropriateelectrical potential across a first conductor disposed on or within theslab waveguide and a second conductor disposed on or within the activelayer, causes the high-speed motion of the active layer toward thesurface of the slab waveguide; actuation is deemed completed when theactive layer can move no closer to the slab waveguide (either in itself,or due to physical contact with the waveguide). To facilitate lightextraction, an array of micro-optical structures (of various possiblegeometries, such as frustums or pyramidal sections, etc.) may beoptionally disposed on the waveguide-facing side of the active layer,such that pixel actuation entails contact or near-contact of thesemicro-optical structures with the waveguide, thus frustrating TIR lightin such a way that re-direction of extracted light to the viewer isoptimized. A more detailed description of micro-optical structures isdisclosed in “Optical Microstructures for Light Extraction and Control”U.S. Pat. No. 7,486,854, which is incorporated herein by reference inits entirety.

Certain other display systems use similar (but not identical) principlesof operation. Some utilize a backlight system where the pixels literallyshutter light, usually by transverse lateral motion of an opaqueMEMS-based shuttering element at each pixel parallel to the main surface(e.g., top surface) of the waveguide configured as a true backlightsystem proper, contra the TIR-based waveguide of Selbrede '491 which isnot a true backlight given the TIR-bound condition of light travelinginside it. For a backlight system, light within the slab waveguideshould not be maintained in a TIR-compliant state lest it be perpetuallybound to the interior of the waveguide. Thus, the bottom surface of thewaveguide can be made a scattering surface, or it can diverge from aparallel spaced-apart relation to the top surface of the waveguide, orboth, to insure that light continually departs the top surface of theslab waveguide to illuminate the pixel shutter mechanisms arrayed at orabove the top surface of the slab waveguide. The appeal of using a slabwaveguide for transverse MEMS shutter-based systems is due to theability to recycle unused light by configuring the waveguide-facingportions of the shutter mechanisms to be nominally reflective. Light notpassing through an open shutter may then re-enter the waveguide and canbe used elsewhere within the system.

In the case of devices based on Selbrede '491, in which the lightsources are arrayed on one edge of the slab waveguide while the oppositeend from said edge is mirrored (with either a metallic reflectordisposed thereon or by imposition of a perfect dielectric mirror to gaineven better reflectance), it has been determined that the luminousuniformity of the display can only be insured when the thickness of theslab waveguide is sufficiently thick. A minimum slab waveguidethickness, t, that can be utilized for the slab waveguide is a functionof the length of the waveguide 1, the critical angle of the waveguideθ_(c) (which is itself a function of the waveguide's refractive index),and the individual optical efficiency of a pixel on the display surface,denoted ∈. The mean free path of a given photon ensemble from origin atthe light source to 99% depletion inside the waveguide is given theGreek symbol λ, which is not to be confused with the optical wavelengthof that light in this context. By detuning the effective individualpixel efficiency ∈, and using the resulting average mean free path of aphoton ensemble prior to 99% depletion, λ, uniformity has beendemonstrated to be readily optimized when λ=31 or greater, therebyestablishing a lower bound on slab thickness by the following equation:

$t = \frac{3 - {\left( \frac{\log (0.01)}{\log \left( {1 - ɛ} \right)} \right)l}}{\left( \frac{{\cos \left( \theta_{c} \right)}{\log (0.01)}}{\log \left( {1 - ɛ} \right)} \right)}$

Applying this constraint to the slab waveguide thickness enablesdisplays based on such waveguides to achieve in excess of 60% opticalefficiency (ratio of light flux input to light flux output) whilesimultaneously insuring far less than 1 dB variation in luminosityacross the entire display surface (typically under 0.2 dB variation).

While this constraint is of minimal consequence for many applications,it does present a step backward for applications where the industrytrend has been toward thinner display subsystems year after year. Thus,for a cell phone, the thickness constraint might require the waveguideto be up to 2 millimeters thick or more to insure outstanding luminousuniformity, whereas the trend in cell phone display components is forthe display to be under 1 mm in total thickness. In actual fact, awaveguide thickness of 0.7 mm is desirable, given that this is astandard thickness for LCD mother glass and TFT active matrix glass.However, so thin a waveguide, by violating the thickness t constraintoutlined above, runs a serious risk of suffering from debilitatingnonuniformities in brightness across the display surface. The symbol tshall hereafter be denominated the minimum slab waveguide thickness thatcorresponds to the minimum luminous uniformity threshold limit.

Recent co-pending filings have disclosed various apodization(compensation) means in orienting and configuring the illumination meansat the edge(s) of the waveguide (e.g., a varying distribution of lightsources along an edge of the waveguide) to resolve luminousnonuniformity. However, the periodicity of the pixels and/ormicro-optical structures disposed on the light extraction surface of thedisplay system (e.g., top surface of the slab waveguide), in conjunctionwith the point source nature of the illumination means (e.g., multiplediscrete LEDs), has given rise to other optically undesirable effects,such as Moire patterns, banding, headlighting (ability to resolve theindividual light sources illuminating the display system), and otherlight artifacts created by using discrete light sources (e.g., LEDs) tofeed light to the waveguide. These light artifacts can be sufficientlysevere as to create liabilities for displays that otherwise may exhibitreasonable macro-level uniformity. It is an object of the presentapplication to address these artifacts at the illumination source bymaking the light entering the waveguide sufficiently diffuse (e.g.,uniform) that the periodic intensity of the original light from theindividual light sources can no longer be individually resolved.

SUMMARY

The problems outlined above may at least in part be solved in someembodiments of the techniques described herein. The following presents asimplified summary of the disclosed subject matter in order to provide abasic understanding of some aspects of the disclosed subject matter.This summary is not an exhaustive overview of the disclosed subjectmatter. It is not intended to identify key or critical elements of thedisclosed subject matter or to delineate the scope of the disclosedsubject matter. Its sole purpose is to present some concepts in asimplified form as a prelude to the more detailed description that isdiscussed later.

The embodiments of the present disclosure provide a light mixing guide(LMG) that may sufficiently diffuse (i.e., mix) light inserted into theLMG from individual (discrete) light sources, such that the insertedlight can no longer be individually resolved, referred to herein as“mixed light”, prior to injecting the mixed light into a primarywaveguide (PW) of a target display system. Various embodiments of thepresent invention provide means to customize the light intensity outputprofile (e.g., linear, non-linear, etc.) that may be subsequentlyinjected into the PW of a target display, in accordance with theparticular luminosity requirements of the target display. The LMG of thepresent disclosure includes a transparent slab waveguide having areflectorized edge, a pair of opposing side edges adjacent to thereflectorized edge, a light transfer edge opposite the reflectorizededge, and a plurality of hollow cavities formed inside the slabwaveguide, wherein at least one of the side edges is configured toreceive light from one or more light sources so that the received lightis totally-internally reflected from top and bottom surfaces of thetransparent slab waveguide. Interaction of the received light with oneor more of the hollow cavities and the reflectorized edge mixes thereceived light prior to the received light passing through the lighttransfer edge and into a target optical system.

The foregoing has outlined rather broadly the features and technicaladvantages of one or more embodiments in order that the detaileddescription that follows may be better understood. Additional featuresand advantages will be described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the claimed subject matter can be obtainedwhen the following detailed description is considered in conjunctionwith the following drawings, in which:

FIGS. 1A and 1B are a top view schematic and a perspective viewschematic, respectively, illustrating a light mixing waveguide adjacenta total internal reflection primary waveguide, wherein a plurality ofcavities have a substantially constant inter-cavity spacing distancebetween adjacent cavities, in accordance with an embodiment of thepresent disclosure;

FIG. 2A is a plan view schematic of a section of a light mixingwaveguide in the vicinity of one of the light sources illustrating lightmixing by depicting light ray splitting (refraction-reflection), andpossible paths of the split light rays, as light interacts with thehollow cavity structures and the reflectorized edge of the LMW;

FIG. 2B is a plan view schematic of an individual cavity within a lightmixing waveguide illustrating both a total internal reflection light rayinteraction with the cavity as well as a refraction-reflection raysplitting interaction with the same cavity to show that both kinds ofinteractions are continually occurring inside the light mixing waveguideto mix the received light;

FIGS. 3A, 3B and 3C are perspective views of a light mixing waveguideillustrating a plurality of hollow cavities having various geometries,further illustrating that the cavities may be through-hole cavities(FIGS. 2A and 2B), wherein each cavity extends from a top surface of theLMW to the bottom surface of the LMW, or the cavities may be embedded(FIG. 2C) inside the LMW;

FIG. 4 is a top view schematic illustrating a light mixing waveguidehaving angled side edges, adjacent a total internal reflection primarywaveguide, in accordance with another embodiment of the presentdisclosure;

FIG. 5 is a top view schematic illustrating a light mixing waveguidehaving reflectors disposed adjacent its two side edges, in accordancewith another embodiment of the present disclosure;

FIG. 6 is a top view schematic illustrating a light mixing waveguidehaving light sources embedded inside the LMW, in accordance with anotherembodiment of the present disclosure;

FIG. 7 is a top view schematic illustrating a light mixing waveguidehaving varying inter-cavity spacing distances between adjacent cavities,in accordance with another embodiment of the present disclosure; and

FIGS. 8A and 8B are a top view schematic and a perspective viewschematic, respectively, illustrating a light mixing waveguide adjacenta total internal reflection primary waveguide, wherein an intercalatedregion between the LMW and the PW may have one or more refractiveindices to adjust the intensity of light (light flux) that enters thePW, in accordance with another embodiment of the present disclosure.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth toprovide a thorough understanding of the embodiments described herein.However, it will be apparent to those skilled in the art that thetechniques described may be practiced without such specific details. Inother instances, detailed physical features are idealized in order notto obscure the techniques described herein in unnecessary detail. Forthe most part, details considering geometric considerations and the likehave been omitted inasmuch as such details are not necessary to obtain acomplete understanding of the claimed subject matter and are within theskills of persons of ordinary skill in the relevant art.

The present disclosure also provides light mixing means to insert lighthaving a desired light intensity (light flux) profile intoedge-illuminated slab waveguides, which delivers distinct advantages indisplay efficiency for several different species of display technology,while avoiding the kind of undesirable optical artifacts arising fromthe interaction of discrete light sources feeding the slab waveguide andthe periodic array of optical shutters (e.g., pixels) or micro-opticalstructures that are often used to extract light from such displays. Alight mixing means and light insertion means is described in the presentdisclosure to cloak discrete light sources (e.g., primary color lightsources) by mixing the light from discrete light sources prior toinserting the mixed light into an edge-illuminated slab waveguide of adisplay. For example, the light mixing and insertion means may beemployed in displays where the pixels modulate light by way of local andselective Frustration of Total Internal Reflection (FTIR) of lighttraveling inside the waveguide. In FTIR-based display systems, the lightmixing means can prevent the aggregation of deleterious opticalartifacts arising out of the interaction of non-uniform intensity lightemanating from periodic discrete light sources and other opticalfeatures (e.g., light-shuttering pixels) that exhibit sufficientperiodicity as to give rise to banding effects, headlighting, Moirepatterns, and/or other undesirable optical effects.

The light mixing means of the present disclosure may be employed indisplay systems that utilize discrete light sources (i.e., point lightsources) to provide the initial light to the display. The light mixingmeans may enable these display systems to deliver their inherent highpower efficiency with excellent luminous uniformity across the displaysurface (regardless of program content) without exhibiting deleteriousperiodicity-based optical artifacts, thereby making such display systemsmore competitive and successful in the marketplace. For example, thelight mixing means may be employed in certain display architectures thatutilize edge-illuminated slab waveguides to provide total internalreflection (TIR) light for FTIR-based displays, FTIR-based backlightsfor LCD panels, and FTIR-based backlights that serve as light recyclingbacklight subcomponents for displays that modulate light using, forexample, transverse optical shutters or equivalent pixel shutteringmechanisms, to name a few, to enhance their optical performance byenhancing luminous uniformity and minimizing optical artifacts.Furthermore, the light mixing means may have utility in other opticalapplications beyond that of TIR-based display systems, and can bevaluable as a general light mixing means as well.

The present disclosure provides a light mixing waveguide that mixeslight from discrete sources (e.g., light emitting diodes (LEDs) orsimilar near-point light sources) in order to create an isotropic ornear-isotropic a desired light flux (e.g., an isotropic light flux) thatmay be inserted into another optical subsystem (e.g., the backlight of aliquid crystal display, or the TIR waveguide that lies at the core ofFTIR-based displays that use the principle of frustrated total internalreflection to turn pixels on and off). For the sake of illustration, thelight mixing waveguide described in the present disclosure isillustrated as being utilized in conjunction with a total internalreflection (TIR) waveguide of an FTIR-based display. However, it is tobe understood that restriction of the description to this specific TIRwaveguide of an

FTIR-based display is not intended to restrict the range ofapplicability of the light mixing waveguide of the present disclosuredescribed herein, which can be incorporated into many other opticalsystems that would benefit from its light mixing properties.

An exemplary FTIR-based display technology to be enhanced, with thelight mixing waveguide disclosed in the present disclosure, is thecurrent iteration of the display technology originally disclosed in U.S.Pat. No. 5,319,491, which is incorporated herein by reference in itsentirety. In this illustrative display system, previously described inthe Background section, pixels emit light using the principle offrustrated total internal reflection within a display architecture thatleverages the principles of field sequential color generation and pulsewidth modulated gray scale creation. Light is edge-injected into aplanar slab waveguide through at least one light injection edge andundergoes total internal reflection (TIR) within the waveguide, trappingthe light inside it due to reflective coatings on the slab waveguide'sedge opposite the light injection edge(s) and TIR on its upper surface,lower surface, and remaining edges. TIR light is contained within thewaveguide by virtue of the waveguide having a refractive index higherthan the square root of two, namely, about 1.4142) and a cladding layer(e.g., air) surrounding the slab waveguide. The TIR waveguide may be arectangular transparent solid usually made of either glass or a suitablepolymer, into which a diffuse or “mixed light” (e.g., isotropic lightflux) needs to be injected at one or more of its edges (i.e., lightinjection edges). Distributed across the waveguide is an array of pixelsthat may be individually controlled to selectively emit light towards aviewer. Each of the plurality of pixels is an electrostaticallycontrolled MEMS structure that propels (i.e., move) a relatively highrefractive index thin film layer, hereafter termed the “active layer”,by controllably deforming the active layer such that at least a portionof the active layer elastically deforms and moves across a microscopicgap (e.g., typically an air-filled gap measuring between 450 to 1000nanometers) into contact or near-contact with the upper surface of theTIR waveguide, at which point light transits across from the waveguideto the active layer either by direct contact propagation and/or by wayof evanescent coupling. The active layer may optionally include an arrayof micro-optical structures on the waveguide-facing surface of theactive layer to enhance the extraction and re-direction of TIR lightfrom the waveguide when any of the array of pixels is actuated to anactivated state.

In conjunction with this illustrative FTIR-based display system, a lightmixing waveguide (LMW) may be utilized to inject “mixed light” into theslab waveguide of the illustrative display system, in order to avoidundesirable optical artifacts otherwise associated with the interactionof discrete light sources and the regular distribution (i.e.,periodicity) of the pixels. The “mixed light” refers to sufficientlydiffuse light that no longer exhibits the periodic light intensityemanating from the discrete light sources. Light from discrete lightsources may be mixed with the LMW of the present disclosure to provide adesired light intensity profile for insertion into a primary waveguide(PW) of an optical display. The LMW may be utilized to provide thedesired light intensity profile at one or more light injection edges ofa primary waveguide in order to provide excellent luminous uniformityacross the display surface (regardless of program content), withoutexhibiting deleterious periodicity-based optical artifacts, therebymaking such display systems more competitive and successful in themarketplace. The utility of the light mixing waveguide is particularlybeneficial to enhance luminous uniformity and minimize undesirableoptical artifacts in displays having a PW thickness less than about 2 mm(e.g., 0.5 to 1.5 mm)

FIGS. 1A and 1B are a top view schematic and a perspective viewschematic, respectively, illustrating a light mixing waveguide 100adjacent a primary waveguide 130 of a target display, for example, theTIR waveguide of the illustrative FTIR-based display system, inaccordance with one embodiment of the present disclosure. The separatelight mixing waveguide (LMW) 100 may be disposed adjacent a lightinjection edge 132 of the primary waveguide (PW) 130 in a spaced-apartrelationship thereby forming a gap 108 therebetween. As previouslydescribed, the PW 130 may be a transparent rectangular solid designed tofunction as a planar waveguide in which injected light is containeduntil total internal reflection (TIR) is frustrated by the pixelmechanism of choice. Typically, the PW 130 has a thickness (z) in arange from about 0.5 mm to 4 mm.

The LMW 100 comprises a transparent slab waveguide 101 having areflectorized edge 102, a pair of opposing side edges 103 adjacent tothe reflectorized edge 102, a light transfer edge 104 opposite thereflectorized edge 102, and a plurality of cavities 105 formed insidethe slab waveguide 101. The waveguide 101 may be a narrow rectangularslab comprising optical-grade glass or polymer. At least one of the sideedges 103 is configured to receive light from one or more light sources120 (i.e., discrete light sources) so that the received light istotally-internally reflected from a top surface 106 and a bottom surface107 of the slab waveguide 101. In general, all surfaces of the LMW areorthogonal or parallel to one another and mechanically smooth (toprevent undue scattering, which would result in light that violatesTIR). The LMW may further comprise a reflector 112 to provide areflective property to the reflective edge 102 to assist in directingmixed light out of the LMW through the opposite light transfer edge 104and into the light injection edge 132 of the PW 130. FIGS. 1A and 1B,then, depict the basic elements that will be further described ingreater detail, and provides a reference for the various embodimentsdescribed herein.

As illustrated, the LMW 100 may have a height or thickness (z′) aboutequal to the height or thickness (z) of the PW 130. In general, thethickness (z′) of the waveguide 101 may be equal to or less than thethickness (z) of the PW 130. Although, to enhance light efficiency andluminosity in the PW 130, preferably the thickness (z′) of the waveguide101 is equal to or nearly equal to the thickness (z) of the PW 130. Itshould be noted that the thickness (z′) of the waveguide 101 may also bethicker than the thickness (z) of the PW 130, however this thicknessdifference may introduce some light loss when light transfers from athicker LMW 100 to a thinner PW 130, which detracts from the efficiencyof the display system. Suitable waveguide 101 thickness (z′) ispreferably similar to the thickness (z) of the PW 130 (e.g., thicknessless than about 4 mm). As previously mentioned, the LMW is particularlyuseful to minimize optical artifacts associated with thinner primarywaveguides having thicknesses less than about 2 mm. As such a preferablerange of the thickness (z′) may be less than about 2 mm, and morepreferably from about 0.2 to 1.5 mm.

The LMW may be mounted to the PW such that the light transfer edge 104and the light injection edge 132 are separated by the gap 108 and inalignment along both their thickness (i.e., height) and lengthdimensions, as illustrated in FIGS. 1A and 1B. The light transfer edge104 of the LMW 100 may be positioned or aligned adjacent the lightinjection edge 132 of the PW 130 such that its length dimension (x′)extends the entire length dimension (x) of the light injection edge 132,thereby mating the LMW's light transfer edge 104 to the PW's lightinjection edge 132. In general, the length (x′) of the waveguide 101 maybe equal to or less than the length (x) of the PW 130. However, toenhance light efficiency and luminosity in the PW 130, preferably thelength (x′) of the waveguide 101 is equal to or nearly equal to thelength (x) of the PW 130. It should be noted that the length (x′) of thewaveguide 101 may also be longer than the length (x) of the PW 130,however this excess length difference may introduce some light loss whenlight transfers from a longer LMW 100 to a shorter PW 130, whichdetracts from the efficiency of the display system. In summary, matchingand aligning the height (z′) and length (x′) dimensions of the lighttransfer edge 104 to the height (z) and length (x) dimensions of thelight injection edge 132 promotes efficient light transfer. Given thesecriteria, the physical slab of glass or polymer forming the waveguide101 could in principle be a very thin rectangle, albeit matched inthickness to the PW 130 (or slightly thinner than the PW) into which theLMW 100 will feed its diffused, fully mixed light.

Preferably, the light transfer edge 104 of the LMW 100 is separated fromthe light injection edge 132 by gap 108. The distance of the gap 108separating the light transfer edge 104 from the light injection edge 132may be in a range from about 1 micron to about 100 microns. However, tominimize light leakage (i.e., light loss) as mixed light travels fromthe light transfer edge 104 to the light injection edge 132, preferablythe distance of the gap 108 is in a range from about 1 micron to 50microns. Ideally, to minimize light loss, the gap 108 may be in a rangefrom about 1 to 10 microns, however in practice this constant gapdistance between the entire lengths (x′, x) of the edges 104, 132 may bedifficult to achieve due to manufacturing challenges. The gap distance108 is greater than about 1 micron in order to avoid evanescenttunneling of light from the light transfer edge 104 to the lightinjection edge 132. Evanescent tunneling of light would undesirablypermit a significant amount of light to short circuit the mixingfeatures (i.e., plurality of cavities 105) thus not fully mixing thelight prior to insertion into the PW 130. Similarly, it should be notedthat the light transfer edge 104 of the LMW 100 may be in contact (i.e.,gap distance 108 is about equal to 0) with the light injection edge 132of the PW 130 when assembled for operation, however this configurationwould also undesirably permit a significant amount of light to shortcircuit the mixing features (i.e., plurality of cavities 105) thus notfully mixing the light prior to insertion into the PW 130.

In general, light from the light sources 120 (e.g., LEDs) is injectedinto the LMW 100 from the side edges 103, wherein a gap 109 between thelight sources 120 and the side edges 103 can insure that onlyTIR-compliant light enters the LMW). The side edges 103 where the lightsources 120 are mounted could conceivably be much smaller in dimensionthan the two long edges, namely the reflectorized edge 102 and the lighttransfer edge 104, although for light efficiency's sake it is usuallyconsidered proper for the light source injection surface (i.e., thesurface area of the side edge 103) to be at least as large as theeffective active surface of the light sources themselves to avoid lossyovershoot of light. It should be noted that the light sources 120 areshown as unitary sources for conceptual purposes, and their preciseposition along edge 103 is a matter of design choice. More than onelight source 120 can be arrayed on a side edge 103, and the single lightsource 120 is shown for the purpose of simplifying the description. Atthis point, it can be appreciated that light traveling from the lightsources 120 (which may be, for example, light emitting diodes or LEDs)can pass through the gap 109 into side edge 103, with the resultinglight now inserted into the LMW 100 traveling at TIR-compliant angleswith respect to the top surface 106 and the bottom surface 107 of therectangular solid slab waveguide 101.

The actual light mixing may be achieved by the plurality of cavities 105formed as integrated features into the physical slab waveguide 101forming the LMW 100. The goal of the LMW 100 is to mix received lighttherein so as to provide a desired light flux profile to the lightinjection edge 132 of the PW 130 via the LMW's light transfer edge 104,without perturbing that light from a strict TIR regime (constraining theangles at which light rays travel within the LMW 100 prior to enteringthe PW 130). Given this criterion, the light rays inserted into the LMW100 from the light sources 120 should substantially avoid encountersthat create angular deviation from TIR compliance. The plurality ofcavities 105 serve as the core means of achieving light mixing. In oneembodiment, the plurality of cavities 105 may be a plurality of hollowcavities that are formed in the waveguide 101. The cavities 105 may behollow (e.g., air-filled, vacuum) or comprise some other material (e.g.,aerogel, silicone) having a refractive index lower than the refractiveindex of the light mixing waveguide 101. One important aspect of thesehollow cavities are that the cavity walls 310 (illustrated in FIG. 3Adiscussed below) are perpendicular to the top surface 106 and bottomsurface 107 of the LMW, and thus parallel to the reflectorized edge 102,the light transfer edge 104, and the two side edges 103 where the lightsources 120 may be mounted. Moreover, the cavity walls 310 are asphysically smooth as possible, to reduce or substantially preventscattering when light encounters the cavity on its journey through theLMW 100. As illustrated in FIGS. 1A and 1B, a linear row of suchcavities 105 may be distributed near the reflectorized edge 102 of theLMW 100 and parallel to that edge 102, and have an inter-cavity spacing(d) distance substantially constant between adjacent cavities, inaccordance with an embodiment of the present disclosure.

In various embodiments described in more detail below, the interspacingbetween the cavities 105 can be either uniform (equidistant) or gradedas a function of distance from the light sources 120 at the side edges103. The cavities 105 may be a wide range of cross-sectional shapes thatcan be selected to optimize light mixing. Moreover, the cavities 105 maybe through-hole cavities that extend from the top surface 106 to thebottom surface 107 of the waveguide 101. Alternatively, the cavities maybe wholly embedded within the waveguide 101. The particular size andcross-sectional shape of the cavities may be designed to optimize themixing process. Moreover, the geometric distribution of these cavities105 inside the LMW 100 may range from simple linear arrays to moreelaborate distributions designed to optimize the mixing process andprovide the desired light flux profile that needs to be transferred tothe particular PW 130.

The reflector 112 may be disposed adjacent the surface of thereflectorized edge 102 and separated therefrom by a gap 113, asillustrated in FIGS. 1A and 1B. Although reflector 112 is shown ascomprising considerable thickness, this is for illustrative purposesonly, and in actual fact the reflector 112 may be a thin sheet ofaluminum or other metallic element preferably positioned in aspaced-apart relationship to the reflectorized edge 102 forming gap 113therebetween. The reflector 112 may also be a substantially perfectdielectric mirror (i.e., within a selected tolerance) comprised of aseries of layers bearing different thicknesses and refractive indices tocreate an even more efficient reflector at edge 102. Alternatively, thereflector 112 may be disposed directly on the surface of therefelectorized edge 102 (not shown). In this embodiment, the reflector112 may be a very thin layer of aluminum or other metallization incontact with the reflectorized edge 102. Moreover, the reflector 112 maybe a dielectric mirror in intimate contact with the reflectorized edge102. Therefore, both variations (reflector 112 disposed directly on thesurface of edge 102, or the reflector 112 in spaced-apart relation tothe surface of edge 102) jointly comprise various embodiments of thisdisclosure.

The principle of operation of the LMW 100 and the plurality of cavities105 is that light can pass from the discrete light sources (e.g., LEDs)on the side edges 103 (most likely through a small air gap 109 to insureTIR compliance) into the waveguide 101 of the LMW 100. When a light rayencounters a cavity (e.g., a hollow cavity), it will either reflect orbifurcate (reflect and refract), depending on the refractive index ofthe waveguide 101 and the angle of incidence the light ray had at thepoint of intersecting the cavity's surface (i.e., cavity wall 310). Apure reflection occurs at angles where TIR is conserved at the cavityboundary, whereas other rays may not be TIR-compliant in the lateraldimension (albeit all rays are intended to be TIR-compliant with respectto the top surface 106 and the bottom surface 107 of the LMW 100 (andthe upper surface and lower surface of the PM 130), referred to hereinas azimuthally TIR compliant. As the rays encounter more and morecavities and interact with them and the reflectorized edge 102 of theLMW, a thorough mixing of the light rays that pass through the lighttransfer edge 104 into the PM 130 will have occurred, creating a verydiffuse and uniform light flux across the light transfer edge 104 of theLMW, in accordance with one embodiment of the present disclosure. Lightthat passes through the light transfer edge 104 of the LMW into the PM,because it is laterally TIR-noncompliant (and azimuthallyTIR-compliant), will be in a highly mixed state (i.e., diffuse light) asa result of the interaction of the light source rays with the pluralityof cavities and the reflectorized edge 102.

FIG. 2A provides a close-up view of the distal end of the light mixingwaveguide 100, inclusive of one of the light sources 120 in spaced-apartrelation to the light injection side edge 103. The possible trajectoryof one light ray, among the countless rays that are continually injectedalong the side edge 103 at many different angles and positions, is shownfor illustrative purposes so that the various interactions of the raywith the cavities 105 and the reflectorized edge 102 depicted in thisembodiment may be better understood. One of the rays illustrated as aray 201 emitted from the light source 120 passes through side edge 103of the waveguide 101 and refracts (i.e., bends) to follow the a new raypath 202, the extent of refraction determined by the refractive index ofthe transparent material comprising the light mixing waveguide 101. Theray 202 then encounters the reflectorized edge 102 and continues on asray 203 until it encounters one of the hollow cavity structures 105, atwhich point the single ray splits into two rays 204, 206 (i.e., areflection-refraction ray split) of potentially unequal intensitiesbased on the laws of optics prevailing at the boundary of the cavity 105(i.e., cavity wall 310). Part of the original ray 203 travels throughthe cavity 105 as ray 204, then encounters the opposite wall of thecavity to refract once again as ray 205, which finally passes throughthe light transfer edge 104 in preparation for entering the lightinjection edge 132 of PW 130, assuming the angle of incidence at theedge 105 permits such action (i.e., lateral non-TIR angle). There may besubsequent ray-splitting events at each cavity wall (i.e., boundary)encountered by the light ray during its journey, and in the interest ofclarity these are not shown. Not only did ray 203 partially refract asray 204 and 205 to exit the waveguide 101, but the remaining energy inray 203 also reflected to form a ray 206 which is shown as being sentback toward the reflectorized edge 102 (or reflector 112), interactingagain with said reflectorized edge 102 and/or reflector 112 to form ray207, which in turn encounters another cavity 105 a to refract through itas a ray 208 and finally ray 209, which undergoes a total internalreflection event at side edge 103 before becoming ray 210 that passesthrough the light transfer edge 104. Additional reflection-refractionray splits, or ray-splitting events, are not shown, but these are knownto occur at each boundary introduced by the cavity walls, exceptingboundaries where total internal reflection occurs (namely, where thesine values of Snell's Law takes on values greater than 1, indicatingthat no refraction is occurring, only reflection is occurring, at thepertinent boundary, based on the intrinsic geometry and ratio ofrefractive indices present at the boundary). Consequently, original ray201 ends up exiting the waveguide 101 as rays 205 and 210, withadditional rays created by ray-splitting events that are omitted fromFIG. 2 a providing even further sets of rays generated from the originalray 201. This process of splitting the rays laterally by the interactionof the light rays with the cavity structures 105 and the reflectorizededge 102 and/or reflector 112 gives rise to exceptionally good lightmixing, creating a very uniform flux of light through the surface of thelight transfer edge 105.

FIG. 2B is a plan view close-up of two different light rays 211, 213encountering a single cavity structure 105, for ease of illustration.Light ray 211 is incident upon the wall of cavity 105 at such an anglethat total internal reflection occurs at the surface boundary of thecavity wall, and the reflected ray 212, of identical intensity with theoriginal ray 211, results. However, an incident light ray 213 encountersthe surface wall of cavity 105 at a different incidence angle than didlight ray 211, such that the ray splits in a reflection-refraction eventat said surface, the reflected portion of the ray forming a newdeparting ray 214, while the refracted portion of the original ray 213forming a new ray 215 that travels through the middle of the cavity'svolume, to encounter the opposite wall of the cavity at an angle thatgives rise to the a ray 216 departing the cavity vicinity through saidwall. There are additional reflection-refraction events at these cavitywall boundaries, which are omitted in the illustration for the sake ofsimplifying the depiction and clarifying the basic difference betweenthe two kinds of ray interaction that are possible at a cavity structureboundary (i.e., cavity wall surface): those two ray interactions beingeither the spitting of the ray into a reflected and refracted ray, orsub-ray, of potentially different intensities whose intensities, whenadded, substantially total the original intensity of the incident wavethat was split in this manner; or the incident ray may undergo totalinternal reflection and not split so that the original ray's energy isdirected into a new reflected ray, such as incident ray 211 reflectingoff of the wall of cavity 105 to form total internally reflected ray212. Note as before that reflection-refraction events can give rise towhat are known as daughter rays, and the daughter rays can generategranddaughter rays upon encountering subsequent cavity walls (i.e.,boundaries) due to the presence of other cavities 105 subsequentlyencountered, as well as the material comprising the light mixingwaveguide.

In applications where the reflector 112 is not applied directly to thereflectorized surface 102 but rather is in a spaced-apart relation tothe surface of edge 102 by a distance of gap 113, the surface ofreflectorized edge 102 may exhibit both total internal reflection itselfin respect to light incident upon it from inside the light mixingwaveguide 101, or ray splitting at reflection-refraction events at thesurface of edge 102, such that light exiting the waveguide at edge 102during such a ray-splitting event may travel across said gap 113 beforeencountering reflector 112 and being diverted back toward edge 102 forre-entry into the waveguide 101. Multiple ray-splittings are possible atedge 102 when the reflector 112 is detached from the surface of edge 102and put in a spaced-apart relationship thereto. However, light (e.g.,laterally non-TIR compliant light) that exits the waveguide 101 throughedge 102 into the gap 113 encounters the reflector 112 and returns tothe waveguide 101. The presence of this optional gap 113, which may befilled with air, vacuum, or some other substance (e.g., aerogel,silicone) with a lower refractive index than that of the waveguide 101,may reduce optical flux losses (e.g., light absorption) that oftenattenuate light rays incident upon metal-blased reflectors. Furthermore,the angular selectivity introduced into the optical behavior of edge 102by introduction of said gap 113 may further enhance the mixing of lightas well. Therefore, although both variations (reflector 112 disposeddirectly on edge 102, or reflector 112 in spaced-apart relation to edge102) jointly comprise the matter covered under this disclosure, it maybe preferable to minimize any light loss due to interaction of lightthat strikes a metallic layer (e.g., metallic reflector 112), byoptionally positioning the reflector 112 in spaced-apart relationship tothe reflectorized edge 102 such that only non-TIR light may strike themetallic reflector 112, as compared to all light (TIR and non-TIR light)when the reflector 112 is disposed in contact with the surface of thereflectorized edge 102.

FIG. 3A illustrates in more detail the through-hole nature of aplurality of cavities 105 that may be formed in the waveguide 101.Moreover, the cavities 105 may be through-hole cavities that extend fromthe top surface 106 to the bottom surface 107 of the waveguide 101. Theinterior surface of the cavities 105 is a cavity wall 310 that issufficiently smooth so as to not cause undue scattering out of the topor bottom surfaces 106, 107 of the waveguide 101, which is perpendicularto interior cavity surface and to the cavity symmetry axis, which arethemselves substantially parallel to the surface of the reflectorizededge 102 and the light insertion edges 103. Moreover, the cavities 105are not restricted to a circular cross-section (i.e., cylindrical hollowcavities passing through the waveguide 101). These idealizations areused for the sake of simplifying the description and are not intended tobe limiting.

Furthermore, regardless of the choice of cross-sectional geometry of thecavities 105 (in this instance, they are shown as circular for the sakeof description), the walls 310 of the cavity should be parallel towaveguide surfaces of edges 103, 102, and 104, and perpendicular tosurfaces 106, 107. When this is the case, light entering the waveguide101 from the light source(s) 120 does not undergo substantialperturbation to non-TIR angles with respect to surfaces 106, 107, butmay be perturbed to non-TIR angles with respect to surfaces 103, 102 and104 after having encountered and optically interacted with any givencavity 105. Furthermore, these light rays may either undergo totalinternal reflection at the boundary of the hollow cavity 105, based onthe angle of incidence upon the cavity wall 310 when the ray encountersit, and based on the ratio of refractive indices between the substancecomprising the waveguide 101 and the air or vacuum or other lowrefractive index material or composition of materials interior to andfilling the cavity 105; or the ray will undergo a reflection-refractionsplit split, with part of the ray traveling through the cavity 105 andanother part of the ray reflecting off the boundary of the cavity. Ineither case, the continual interaction of light rays with the pluralityof cavities 105 causes the light to become further mixed and moreisotropic, through the above-identified process of TIR reflection orreflection-refraction splitting, a phenomenon also known colloquially asray-splitting. Such light will also interact with the reflector 112 aswell as with the plurality of cavities 105, so that the lightdistribution approaches a sufficiently mixed and isotropic form totravel through the light transfer edge 104 into the PW 130 through thelight injection edge 132. There will be a suitable boundary between 104and 132, as noted earlier, comprised either by an explicit air gap orother such gap, or a boundary demarcated by a material difference in theindex of refraction between 104 and 132 if they should be abutted one tothe other. Such a boundary provides the best light mixing behavior andthus constitutes a preferred embodiment, since it forces light back tothe cavities 105, so that only light that has been mixed by interactionwith one or more of the plurality of cavities 105 is able to finallypass through the boundary between 104 and 132. However, it is possibleto have no appreciable boundary difference between 104 and 132, but suchan architecture will only mix approximately half of the light beinginjected into the light mixing waveguide from the light sources 120since about half of the inserted light will entirely bypass interactionwith the cavity structures 105 that give rise to the desired lightmixing behavior.

FIG. 3B illustrates the fact that the techniques described herein arenot tied to any particular cross-sectional geometry or shape for thehollow cavities that do the TIR reflection or reflection-refractionsplitting, and thus achieve the desired mixing of the light beingprocessed by the LMW 101. In this instance, the cross-sectional area ofthe hollow cavities is a square, and the respective square column-shapedcavities 302. Other possible shapes for the cross-sectional geometry forthe hollow cavities are triangular, rectangular, elliptical, hexagonal,pentagonal, octagonal, or other cross-sectional shapes. Although it isexpected that fabrication and manufacturing exigencies are more likelyto favor circular cross-sections that provide cylindrically-shapedhollow cavities passing through the waveguide 101. The cavities 105 maybe a wide range of cross-sectional shapes and sizes that can be selectedto optimize light mixing. For example, the size of the cavities 105 maybe in a range from about 0.1 mm to about 5 mm.

FIG. 3C illustrates that the cavity 303 may be completely embeddedinside the waveguide 101. Other configurations of cavities embedded inthe waveguide 101 are also possible, and these alternate configurationscan serve to optimize light mixing in various ways, while the actualsize of the cavity is similarly optimized.

By the same token, the illustrated embodiments are not limited to havingeach of the cavities 105, 302 comprising the plurality of cavities to befilled with the same material (e.g., air, vacuum, or material ofspecific refractive index), and it conceivable that varying thecomposition of the cavity's contents from one cavity to the next canaccrue to the optical benefit of the mixing process by altering theoptical behavior as a function of position within the light mixingwaveguide 101. Furthermore, the illustrated embodiments are not limitedby having an isotropic material filling any given cavity, but any givencavity could have more than one refractive index material within it,arranged as desired (either with discrete boundaries between materialsor a gradient from one refractive index to another), if such internalcompositional variety inside the cavity provides optimal optical lightmixing performance not otherwise obtainable from an isotropic interiorof the cavities 301.

There are alternative embodiments that angle the side edges that areused for light injection in order to alter or optimize the angulardistribution of light in the waveguide 401, which can be varieddepending on the output requirements. For example, the rectangular shapeof waveguide 101 in FIG. 1A may be trapezoidal, as illustrated in FIG.4, or formed another polygonal structure (e.g., square, pentagon,hexagon, etc.), since the light mixing will occur in that instance aswell. The narrow rectangular shaped waveguide 101 is selected both forillustrative purposes and because it is likely to represent the lowestpossible use of available space for such a LMW 100. FIG. 4 illustratesthat side edges 403 may be angled (i.e., angled sides of a trapezoid),and furthermore, that the one or more light sources 420 may be angledadjacent the angled side edges 403 in order to inject lightperpendicular to angled side edge 403 and direct the initial light fromthe discrete light sources 201 into the waveguide 401 and towards one ormore cavities 105 therein, thereby increasing the mixing efficiency ofthe LMW 400. However, it should be noted that angled light sources 420need not inject light perpendicular to angled side edges 403. Forexample, the angled light sources 420 depicted in FIG. 4 may substitutethe light sources 120 depicted in FIG. 1A in order to inject light intothe side edges 103 of rectangular waveguide 101 at an angle with respectto the normal perpendicular to the surface of side edge 103. Injectedlight can be angled to improve or alter efficiency or flux distributionas light from discrete light sources 120 is introduced into the LMW 100.

It should be noted that the efficiency of any light mixing means is alsoa function of light leakage, and that there are potential locations inthe LMW 100 where leakage might occur, such as at side edges 103, sothat reflective means may be imposed on such surfaces, or be associatedwith the light sources 120 themselves, albeit not in such a way as toocclude any light source injecting light into the slab waveguide 101, soas to contain as much light as possible inside the waveguide 101 so thatthe mixed light's primary departure route is out through the lighttransfer edge 104 and into the PW 130 through edge 132, as illustratedin FIG. 5. In another aspect, light sources 502 need not be located onboth edges 103 but can be added on only one edge 103 with the opposingedge being itself reflectorized by reflective element 501, asillustrated in FIG. 5. In the case of mating a single light source toone of the side edges, the opposing side edge would also be a reflectivesurface. It is further noted, that with only one edge illuminated, thecavities may be adjusted in density, distribution, size, andinterspacing, to insure an isotropic flux under such a light injectionscenario.

There are also alternative embodiments that allow for the light sourceto be embedded into the LMW 600, as illustrated in FIG. 6. Light sources620 may be embedded inside the waveguide 601 (e.g., near the 103 sideedges or elsewhere in the LMW) as illustrated in FIG. 6, rather thanbeing disposed outside the LMW in spaced-apart relationship with an airgap therebetween as previously depicted with respect to FIGS. 1A and 1B.A reflective shield surrounding at least a portion of each of theembedded light sources 620 may be introduced (not shown) to insureTIR-compliance of such injected light being imposed, if needed.

In another aspect, FIG. 6 also illustrates that reflector 112 may beapplied directly to the surface 102, rather than in a spaced-apartrelation to surface 102. The reflector 112 in contact with surface 102may impart excellent reflective properties to the surface 102, howeverthere is a certain amount of light attenuation (i.e., light loss) due tolight rays incident upon metal-biased reflectors. To minimize lightloss, the reflector 112 may be in a spaced apart relationship to surface102 with this optional gap 113, to reduce optical flux losses that oftenattenuate light rays incident upon metal-biased reflectors, aspreviously described with respect to FIGS. 1A and 1B.

In another embodiment, the plurality of hollow cavities in the LMW areconfigured to provide some level of apodization, which may serve toimprove luminous uniformity within the waveguide. It is understood thatthe LMW 100 is a light preprocessor and that more than one edge of thePW 130 may have an associated LMW 100 mounted to it, as displayexigencies may require. As a consequence of configuring the LMW 100 forapodization, light flux (i.e., intensity of light) entering the PW 130may no longer be spatially isotropic, but may exhibit a gradient orother desired profile. The gradient may be desirable because lightinjected from the LMW 100 into the PW 130 may undergo depletion as ittravels through the array and encounters activated pixels. Apodizationcan compensate for any such depletion effects, and where it is desirablethat such apodization be applied, the LMW can be configured to achievethe desired apodization by geometrically configuring the plurality ofhollow cavities in a suitable manner The specific nature of theapodization gradient (linear, exponential, tuned to the pixelefficiencies present on the display surface, etc.) is adjusted tomaximize uniformity in any given display setting. These representdifferent optimization schemas for this embodiment, and are variationsintended to tune the performance of any given display system to optimizethe luminous uniformity.

Referring now to FIG. 7, apodization of the light being ejected by theLMW 101 or 701 through its light transfer edge 104 can be achieved bysuch geometric strategies as defined above, by suitable selection of theposition and size of the cavities so as to create more light flux insome parts of the light transfer edge 104 and less light flux in otherparts of the light transfer edge 104, which is a feature that can becalled for in display systems based on frustrated TIR which tend todeplete light across the display surface; such light depletion can becompensated for by apodization of the light sources. In this instance,the apodization is applied not to discretized point sources but ratherto the highly mixed flux that the waveguide 701 creates from the initiallight injected into the LMW from the light sources (120, or 720, 721,and/or 722, etc., as required). Therefore, apodization can be used toprovide compensation of flux intensity for light entering the PW 130 toimprove the luminous uniformity of displays that exhibit light depletionas a function of distance from the light source and the number ofactuated pixels injected light encounters prior to total depletion.

The inter-cavity spacing (d) between the cavities can be either uniform(equidistant) or graded as a function of distance from the light sources120 at the side edges 103. FIG. 7 illustrates different possiblearchitectural arrangements in respect to both the light sources (e.g.,LEDs) and their respective distribution along the edges 104 of thewaveguide 701, as well as in respect to the interspacing and spatialdistribution of the cavities 705, 706, 707, 708 formed inside thewaveguide 701. For example, the plurality of cavities 105 depicted inFIGS. 1A and 1B illustrate one possible embodiment that indicates therelative positions of a plurality of cavities 105 that are formed insidethe waveguide 101. The distribution of the cavities 105 are shown asbeing collinear with an equidistant inter-cavity spacing (d), and nearerreflectorized edge 102 (and its associated reflector 112) than they areto the light transfer edge 104. Alternative embodiments may use otherarrangements of the plurality of cavities. Alternative embodiments arenot limited to this geometric distribution of the cavities, nor arethese embodiments restricted to any given quantity or size of cavities105, so long as the ray splitting gives rise to the targeted amount oflight mixing. For example, a light mixing waveguide 700 depicted in FIG.7 illustrates a transparent waveguide 701 having cavities 705 (e.g.,hollow air-filled cavities) are spaced farther apart toward the distiltermini edges 103, and closer together toward the center of thewaveguide 701. Although shown as collinear, they need not be collinearand can be distributed in any orientation that provides good lightmixing. Furthermore, it is also possible to position certain cavities707 in other locations within the waveguide 701, which may serve toredirect light more favorably toward the reflector 112 and/or othercavities 708.

The interior composition of the cavities 705, 706, 707, 708 need not beisotropic and uniform if an anisotropy in refractive index inside thecavities leads to optical benefits in regard to light mixing, nor arethe illustrated embodiments limited to having each of the cavitieshaving the same shape, the same size, or the same interior compositionand/or refractive index. Furthermore, while a preferred embodiment callsfor the walls of the cavities 705, 706, 707, 708 to be perpendicular tothe top surface 106 of the waveguide 701 and, consequently, parallel to103 and 104, for the purpose of insuring that incident light raysencountering said cavities do not perturb away from angles that complywith total internal reflection within the interior of the slab waveguide701, alternative embodiments are not limited to such a geometricrestriction, which may be called for in certain instances when theperturbation of rays does not present a significantly deleterious sideeffect in regard to system noise level or contrast ratio degradation.

FIG. 7 shows a multiplicity of light sources 720, 721, and 722, that maybe used to replace the single light source 120 abutted on the edge 104depicted in FIGS. 1A and 1B. It is possible, in some situations, forlight source 720 to correspond to one primary color, 721 to anotherprimary color, and 722 another primary color; or they can all bemultiple-light-source systems to begin within, and arrayed along theedge(s) 103 due to geometric, optical, mechanical, and/or thermalconsiderations that dictate the use of smaller LEDs to fill edge 103. Itis common in the art to try to fit the insertion face of an LED to theedge of the waveguide into which its light is to be inserted, to avoidovershoot and other lossy effects. The techniques described herein arenot limited to either one or three LEDs, but to any illumination sourcesof any kind that are arrayed along the side edges 103. The examplesshown in both LMWs 100 and 700 are for illustrative purposes only andare not intended to limit the all embodiments to these specificallyquantified pluralities of light sources, nor are all embodiments tied toany specific location of the light sources 720, 721, and/or 722 or 120along the edge(s) 103.

FIG. 8 illustrates an alternative embodiment wherein the air gap betweenthe light transfer edge 104 and the light injection edge 132 of the PW130 is filled with an intercalated region 800 having one or morespecific refractive indices. Region 800 represents an intercalatedinterstitial region between the PW 130 and the waveguide 101 that may beconfigured with respect to its refractive index, particularly inreference to the ratio of region 800 refractive index to the refractiveindex of the waveguide 101, and the ratio of region 800 refractive indexto the refractive index of the PW 130. It is to be noted that whileregion 800 can be uniform and isotropic with respect to its refractiveindex, this is not a restriction on all embodiments, and to illustratethe significance of this fact, the region 800 has been shown divided(arbitrarily, for the sake of illustration only) into three discreteregions, 801, 802, and 803. In this example, discrete regions 801 and803 of element 800 have a lower refractive index than the middlesubelement 802, with the result that light passing into region 800 fromthe waveguide 101 through light transfer edge 104 will have greater fluxtransfer into the higher refractive index region 802 than it willthrough the lower refractive index regions 801 and 803. This differencein transfer efficiency across the boundary from edge 104 to therespective discrete regions of 800 (discrete regions 801, 802, and 803)is premised on the different critical angles presented to light thatencounters the boundary between 104 and 800 after having traveledthrough the waveguide 101. The potential benefit of subdividing region800 into discrete subregions bearing different refractive indices isthat such variable refractive index regions serve to apodize and adjustthe intensity of light entering the PW 130 based on the position alongthe edge 132 that the light enters, which can serve to improve theluminous uniformity of the light available to the primary waveguide foruse in the final application (whether that be a TIR-based waveguide, abacklight for an LCD system, or other application). It should be notedthat the partitioning of the region 800 into three discrete subregionsis purely arbitrary, and that the region 800 can be divided into anynumber of regions. Alternatively, instead of discrete regions withinregion 800, a smooth gradient of refractive index within the region 800may be used to achieve apodization of light being transferred from thewaveguide 101 into the PW 130 as the light passes through the lighttransfer edge 104 into region 800 to be potentially apodized and thenpassing into the PW 130 through the light injection edge 132. Therefore,region 800 can bear a uniform refractive index chosen for its criticalangle, it can bear different partitioned subregions withindividually-tuned refractive indices, or it can be manufactured with atargeted gradient in its refractive index composition. The thickness ofthe region 800 as it fills the space between light transfer edge 104 andlight injection edge 132 is arbitrary and is expected to be small forpractical reasons, although in alternative embodiments any givenspaced-apart relation between 104 and 132 (and consequently, any giventhickness of region 800, however it may be composed) may be used.

It should be understood that the general principle described herein, theuse of cavities 105, to achieve ray splitting to facilitate lightmixing, is not only suitable for mixing primary colors (e.g., red,green, and blue, which may correspond, for illustrative purposes, to therespective light sources 720, 721, and 722), but it may also be suitablefor general optical applications where light mixing is required,including automotive applications, avionic applications, generallighting applications, display applications, etc. Its value in removingoptical artifacts associated with the interaction of discretized lightsources with an array of pixels or micro-optical structures is importantin one specific area of art, but this does not limit the range ofapplicability of the techniques described herein. The specific detailsprovided are for illustrative purposes only and should not be read asrestricting the scope of the claimed subject matter.

Embodiments of the techniques described herein can enhance the luminousuniformity of display systems comprised of edge-illuminated slabwaveguides that are thinner than the uniformity threshold limit (t)without incurring undesirable optical artifacts arising out of thegeometric interaction of point sources with the array of pixels ormicro-optical structures associated with the pixel actuation mechanism.The various embodiments described herein can be implemented on a host ofdisplay systems that could be expected to use edge-illuminated slabwaveguides and/or associated light-recycling backlight subsystems orFTIR-based display technologies and would thus would be highly desirableand lead to improved image generation by system architectures based onsuch planar illumination architectures. These embodiments may alsofacilitate the mixing of primary color lights (e.g., red, green, andblue) and can also be extended to more general optical and lightapplications where the smooth mixing of point sources of lights (e.g.,LEDs) into a uniform flux, or other desired light flux profile, passingthrough the surface of the light transfer edge is desirable.

It will be seen by those skilled in the art that many embodiments takinga variety of specific forms and reflecting changes, substitutions, andalternations can be made without departing from the spirit and scope ofthe invention. Therefore, the described embodiments illustrate but donot restrict the scope of the claims.

1. A light mixing system comprising a transparent waveguide having areflectorized edge, a light input edge adjacent to the reflectorizededge, a light output edge opposite the reflectorized edge, a pluralityof cavities formed inside the waveguide, and two or more light sourcesof different colors, wherein the light input edge receives light ofdifferent colors from the light sources and the received light ofdifferent colors is totally internally reflected from opposite majorsurfaces of the waveguide, wherein the cavities are bounded by wallsthat are substantially parallel to the edges and substantiallyorthogonal to the major surfaces of the waveguide to reduce scatteringof the received light of different colors out of the major surfaces, andwherein interaction of the received light of different colors with oneor more of the cavities and the reflectorized edge mixes the light ofdifferent colors before exiting the light output edge.
 2. The lightmixing system of claim 1, wherein the cavities are filled with amaterial having a refractive index that is different from the refractiveindex of the waveguide.
 3. The light mixing system of claim 1, whereinthe cavities are filled with a vacuum, air or other material having alower refractive index than the refractive index of the waveguide. 4.The light mixing system of claim 3, wherein the cavities are filled withaerogel or silicone.
 5. The light mixing system of claim 3, wherein thematerial filling the cavities is varied.
 6. The light mixing system ofclaim 1, wherein the cavities are through-holes extending between themajor surfaces of the waveguide.
 7. The light mixing system of claim 1,wherein the cavities are embedded inside the waveguide.
 8. The lightmixing system of claim 1, wherein at least one of the light sourcesemits light of a primary color.
 9. The light mixing system of claim 1,wherein the light sources emit red, green and blue light.
 10. The lightmixing system of claim 1, wherein the waveguide is a planar slabwaveguide.
 11. The light mixing system of claim 10, wherein thewaveguide is a narrow rectangular slab.
 12. The light mixing system ofclaim 1, wherein the waveguide is made of optical-grade glass orpolymer.
 13. The light mixing system of claim 1, wherein the cavitieshave smooth walls.
 14. The light mixing system of claim 1, wherein thewaveguide is attached to a backlight of a display system.
 15. The lightmixing system of claim 14, wherein the display system is a liquidcrystal display.
 16. The light mixing system of claim 1, wherein thelight exiting the light output edge of the waveguide enters a lightinjection edge of a primary waveguide.
 17. The light mixing system ofclaim 16, wherein the primary waveguide is a backlight of a displaysystem.
 18. The light mixing system of claim 17, wherein the displaysystem is a liquid crystal display.